1. Field of the Invention
The present invention relates to a molding machine having a drive unit for rotating and reciprocating a movable body, such as a screw.
2. Description of the Relevant Art
An in-line screw injection molding machine equipped with a motor drive unit for rotating and reciprocating a screw is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 9 (1997)-11290.
Such an injection molding machine includes a measurement-related drive section, which employs a first servomotor and is adapted to rotate a screw, and an injection-related drive section, which employs a second servomotor and is adapted to reciprocate the screw. In a measuring step, the measurement-related drive section causes the screw to rotate, thereby plasticizing and measuring a molding material. In an injection step, the injection-related drive section causes the screw to advance, thereby injecting and charging the measured resin into a mold. Many molding machines employ a drive unit for driving a movable body, such as a screw, in two different operation modes as mentioned above.
However, since such a drive unit employs one servomotor for each drive section, as many servomotors as drive sections are required. Further, the drive section for reciprocating the movable body requires not only a servomotor but also a motion conversion mechanism, such as a ball screw mechanism, in order to convert the rotational motion of the servomotor to a linear motion. As a result, due to an increase in the number of components, the overall structure of an injection molding machine becomes complicated and increases in size, resulting in an impairment in reliability and a great increase in overall cost.